This invention relates to by-pass valves for heat exchanger circuits in which there is a cooler or cooler unit for a heat exchange fluid.
In the automotive industry, for example, heat exchangers are used to cool or heat certain fluids, such as engine oil or transmission fluid or oil. In the case of transmission fluid for instance, a heat exchanger, which can be called a cooler, is used to cool the transmission fluid. The heat exchanger is usually located remote from the transmission and, in normal operating conditions, it receives hot transmission oil from the transmission through supply tubing, cools it and delivers it back to the transmission through return tubing. However, when the transmission is cool, such as at start up conditions, the transmission oil or fluid is very viscous and does not flow easily through the heat exchanger, if at all. In such cases, the transmission can be starved of oil and this may cause damage or erratic performance. Cumulative damage to the transmission can also occur if the quantity of oil returned is adequate but is over cooled due to low ambient temperatures. In this case, for instance, moisture condensation in the oil (that would otherwise be vaporized at higher temperatures) may accumulate and cause corrosion or oil degradation.
In order to overcome the cold flow starvation problem, various solutions have been proposed in the past. One solution is to use a by-pass path between the heat exchanger supply and return lines, often with a heat actuated by-pass valve located in the by-pass path. An example of a by-pass valve is shown in U.S. Pat. No. 6,253,837 issued Jul. 3, 2001 to Long Manufacturing Ltd. Using a thermal by-pass valve to by-pass a cooler can provide rapid warm up of the oil or fluid, which in addition to addressing the concerns noted above can also result in improved fuel economy.
U.S. Pat. No. 5,791,557 issued Aug. 11, 1998 to Behr Thermot-tronik GmbH & Co. describes another form of thermostatic valve which provides a by-pass capability. This valve includes a valve housing and a preassembled construction unit insertable into the housing. The construction unit includes a thermostatic working element with a restoring spring and movable valve elements. The collar of the working element forms a valve slide for an inflow valve which, under cold conditions, blocks the connection of the inflow between an inlet and an outlet. A lower section of the valve chamber is used as a by-pass duct which can be blocked off by means of a by-pass valve in the direction of a return flow. The by-pass valve includes a by-pass valve seat and a by-pass valve disk. The seat is moulded to a holding part which is fitted into a section of the chamber of the housing.
In one known form of by-pass valve arrangement for an automotive transmission wherein the by-pass valve is connected to a cooler by means of an outlet port located at one end section of the valve chamber and by means of an inlet port located at an opposite end section of the valve chamber, a thermally sensitive actuator or wax motor is disposed in the valve chamber so that it has a first end located in the one end section and a second end disposed towards the opposite end section. A piston extends from the first end of the actuator and engages the adjacent end of the valve chamber by projecting into a suitable recess. A valve seat is located in the valve chamber adjacent the second end of the actuator and this seat extends around a by-pass port which can be closed or opened by means of an annular valve ring mounted for sliding movement on the actuator body. A return spring extends through the by-pass port and engages the second end of the actuator body, thereby urging it away from the valve seat.
A difficulty with this forward flow arrangement for a by-pass valve is that there is no provision for pressure relief in the event of excessive pressure build up in the one end section of the valve chamber that contains the actuator. It is desirable to provide a pressure relief capability in order to avoid undue wear on or possible failure of components in the by-pass valve unit and also to help avoid premature wear on or failure of the cooler unit.